1. Field of the Invention
The present disclosure relates to a ring main unit (so called abbreviated as RMU), and particularly, to an arc extinguishing apparatus for a ring main unit.
2. Background of the Invention
A multi-circuit switchgear so called as the ring main unit is the electric power device for using to branch the electric power from an electric power line (that is an electric power cable) laid under the ground and distribute it to an electric consumer such as a building on the ground or to divide the electric power.
The ring main unit includes an outer case charged with an arc-extinguishing gas for extinguishing an arc therein, incoming power lines for Alternating Current (abbreviated as AC hereinafter) 3 phases (in other words 3 poles) led into the outer case from the underground electric power line, outgoing power lines for a plurality of branch lines connected from the outer case to a plurality of electric loads (or consumers), and a switch mechanism for electrically switching to a connecting position that connects the incoming power lines with the outgoing power line for a branch line, earthing position for earthing (or grounding) the power lines or separation position that separates the incoming power lines from the outgoing power line.
An example of the ring main unit according to the related art will be described with reference to FIGS. 1 to 7.
First, a configuration of an arc-extinguishing apparatus of the ring main unit according to an example of the related art will be described.
The disclosed related art cites the disclosure of U.S. Pat. No. 4,803,319, and a more detailed configuration and operation may be referred to the publication of U.S. Pat. No. 4,803,319.
The ring main unit according to an embodiment of the related art is configured to include an outer case 1, a first bushing 10a, a second bushing 10b, a first fixed contact 2, a permanent magnet 7, a second fixed contact 3, a first bus bar 4, a second bus bar 5, an upper insulator 6a, a lower insulator 6b, a rotational shaft 8, a movable contact 9, a support frame 12, and an insulating gas 11.
In FIG. 1, reference numeral 15 denotes an arc generated between contacts when the movable contact 9 is separated from the first fixed contact 2 and the second fixed contact 3 while an electric current flows, and reference numeral 16 denotes a magnetic field generated in the vicinity of the permanent magnet 7 by the permanent magnet 7.
In FIG. 2, reference numeral 13 denotes an insulating partition wall for electrically insulating electric power circuit for each phase in order to prevent short circuit between phases.
Also, reference numeral 15a in FIGS. 4 and 6 designates a high temperature and high pressure arc vapor moving as ambient air is heated by the arc 15.
The outer case 1 determines an external appearance of the ring main unit and is provided as a means for accommodating or supporting the configuring components of the ring main unit. As shown in FIGS. 1 and 2, the outer case 1 is made of a metal whose vertical section is a rectangular shape or a circular shape.
The first bushing 10a is a terminal unit fixedly installed on an upper portion of the outer case 1. The first bushing 10a has an electrical conductor member therein and is formed by molding an electrical insulating material on the outside thereof such that incoming power lines of respective AC phases such as an R phase, an S phase, and a T phase led into the outer case 1 from the underground power line. As shown in FIG. 2, three first bushings 10a may be provided to correspond to the three AC phases, respectively.
The second bushing 10b is a terminal member fixedly installed on a lower portion of the outer case 1, to which outgoing power lines for a plurality of branch lines connected from the outer case 1 to the electric loads (or consumers) are connected. Like the first bushing 10a, the second bushing 10b includes an electric conductor member therein and is formed by molding an electric insulating material on the outside thereof. Three second bushings 10b may be provided to correspond to three AC phases in each of the branch circuit.
The first fixed contact 2 is a fixed contact portion electrically connected to the first bushing 10a through the first bus bar 4 and is configured by an electric conductor blade.
As shown in FIG. 5, the permanent magnet 7 is inserted into an end portion open to both sides, that is, into an accommodation recess portion formed in both end portions of the first fixed contact 2 and supported therein, and a cover 14 may be installed to prevent the permanent magnet 7 from being released downwardly.
As shown in FIG. 2, three first fixed contacts 2 may be provided to correspond to the three AC phases, respectively.
The permanent magnet 7 is a means fixedly installed in the end portion of the first fixed contact 2 and for applying a magnet field 16 to extinguish the arc 15.
The second fixed contact 3 is an electric load side fixed contact portion electrically connected to the second bushing 10b through the second bus bar 5, and is configured by an electrical conductor blade. As shown in FIG. 2, three second fixed contacts 3 may be provided to correspond to three AC phases, respectively.
The first bus bar 4 is an electrical conductor that electrically connects the first fixed contact 2 to the first bushing 10a. For example, the first bus bar 4 may be made of a copper material and configured as a thin wide bar.
The second bus bar 5 is an electrical conductor that electrically connects the second fixed contact 3 to the second bushing 10b. For example, the second bus bar 5 may be made of a copper material and configured as a thin wide bar.
The upper insulator 6a is an insulating support member made of an electrically insulating material and supporting the first bus bar 4 such that it is electrically insulated from the support frame 12.
The lower insulator 6b is an electrically insulating support member made of an electrically insulating material and supporting the second bus bar 5 such that it is electrically insulated from the support frame 12.
The movable contact 9 is configured by an electrical conductor and supported to be rotatable by the rotational shaft 8. The movable contact 9 is a rotatable unit that is rotatable to a circuit closing position (or an ON position) in which the movable contact 9 is in contact with the first fixed contact 2 and the second fixed contact 3 to switch the 3-phases electric power circuit between the electric power source side and the electric load side of each branch circuit into a closed circuit state, or to a circuit opening position (or an OFF position) in which the movable contact 9 is separated from the first fixed contact 2 and the second fixed contact 3 to switch the 3-phases electric power circuit into an open circuit state.
As shown in FIG. 2, the three movable contacts 9 are commonly supported by the rotational shaft 8 so as to be rotated, and three movable contacts 9 may be provided to correspond to the 3-phases electric power circuits.
The rotational shaft 8 is a driving unit for supporting and driving the movable contact 9 to the circuit opening position or the circuit closing position. The rotational shaft 8 is connected to an electric motor (not shown) or a manual driving source (not shown) and rotated in a clockwise direction or counterclockwise direction.
The support frame 12, which is a means for supporting the upper insulator 6a, the lower insulator 6b, and the rotational shaft 8, is fixedly installed in the outer case 1.
The operation of the ring main unit according to an example of the related art configured as described above will be described with reference to FIGS. 1 to 7.
First, an operation from the circuit opening position (OFF position) as can be seen in FIGS. 1 to 4 to the circuit closing position as can be seen in FIG. 3 will be described.
When the rotational shaft 8 is rotated by an electric motor (not shown) or a manual driving source (not shown) in the clockwise direction, the movable contact 9 goes into a position in which it is in contact with the first fixed contact 2 and the second fixed contact 3 according to driving of the rotational shaft 8.
Thus, an underground power line for the electric power source side electrically connected to the first fixed contact 2 through the first bus bar 4, the first bushing 10a, and an incoming power line for each phase (not shown) is electrically connected to the electric load side power line of a branch circuit electrically connected through the movable contact 9, the second fixed contact 3, the second bus bar 5, the second bushing 10b, and an outgoing electric power line for each phase (not shown), and thus, electric power may be supplied from the underground power line to the branch circuit.
Next, an operation from the circuit closing position (or an ON position) as can be seen in FIG. 3 to the circuit closing position (or an OFF position) as can be seen in FIGS. 1 to 4 will be described.
When the rotational shaft 8 is rotated by an electric motor (not shown) or a manual driving source (not shown) in the counterclockwise direction, the movable contact 9 goes into a position in which it is separated from the first fixed contact 2 and the second fixed contact 3 according to driving of the rotational shaft 8.
Thus, the underground power line for the electrical power source side electrically connected to the first fixed contact 2 through the first bus bar 4, the first pushing 10a, and an incoming power line of each phase (not shown) is electrically separated from the electric power line of the electric load side of the branch circuit electrically connected through the movable contact 9, the second fixed contact 3, the second bus bar 5, the second bushing 10b, and an outgoing power line for each phase (not shown), and the electric power supply to the branch circuit from the underground power line is interrupted.
In the case of the interrupting operation, the arc 15 occurs between the first fixed contact 2 and the movable contact 9, and the high temperature and high pressure arc vapor 15a is generated in the vicinity of the arc 15. At this time, as can be seen in FIGS. 4 and 5, electromagnetic force F as shown in FIG. 4 is generated by a current I and the magnetic field 16 according to Fleming's left hand rule. Such electromagnetic force F acts to push the arc 15 between the first fixed contact 2 and the movable contact 9, so the arc 15 between the first fixed contact 2 and the movable contact 9 is pushed out to become extinct.
However, as the circuit closing operation or the circuit opening operation is frequently performed, the high temperature and high pressure arc vapor 15a is attached to the first fixed contact 2 and the upper insulator 6a to contaminate and damage the first fixed contact 2 and the upper insulator 6a and cause insulation breakdown between the first bar 4 and the support frame 12. Also, as the density of the high temperature and high pressure arc vapor 15a in the insulating gas 11 is increased, insulation performance of the insulating gas 11 and electrical insulation properties between the outer case 1 and the insulating gas 11 are degraded, and in the case of circuit opening operation, electrical insulation properties between the first fixed contact 2 and the second fixed contact 3 and insulation properties among the R, S, and T phases are degraded.